Method for making armature-commutator assembly having armature winding of very small diameter

ABSTRACT

Apparatus and method for making an armature-commutator assembly having an armature winding wire of very small diameter comprising forming a plurality of wire-engaging fingers on the commutator, engaging a plurality of insulated conductors led out of the armature winding with the fingers, applying equal pressure simultaneously to all the engaging portions by a plurality of electrode bars whose number is equal to the number of the fingers and which have at their engaging end a recess portion of a depth which is approximately equal to the diameter of the comductor, and while continuing to apply that pressure, supplying to the electrode bars either equal valued currents simultaneously, or successively reduced currents sequentially for electrically connecting the fingers with the conductors.

O United States Patent 1 1 1111 3,781,981 Miura et al. 1 Jan. 1, 1974METHOD FOR MAKING 2,572,956 10 1951 Servis 29/597 ARMATURECOMMUTATORASSEMBLY 2,791,667 5/1957 Clark et al. 310/234 X 3,421,212 1/1969 Chabot29/597 X wlNDlNG 0F VERY 3,156,037 11/1964 Warner 29/597 X [75]lnventors: Tatuo Miura; Toshiro Kaneko, both Primary Examiner-Richard J.Herbst I of Kariya, Japan Assistant Examiner-Carl E. Hall [73] Assignee:Nippondenco Co., Ltd., Kariya-shi, Atmmey john Maney et Japan A [22]Filed: Feb. 28, 1972 [57] BSTRACT Apparatus and method for making anarmature- [2l 1 App! 229,991 commutator assembly having an armaturewinding Rehted s Appncafion Dam wire of very small diameter comprisingforming a plu- [63] Continuation-impart of Ser. No. 810 238 March 25rality of wire-engaging fingers on the commutator en- 1969. abandoned 3gaging a plurality of insulated conductors led out of the armaturewinding with the fingers, applying equal [52] Cl 29/597, 29/205 C 29/205CM pressure simultaneously to all the engaging portions by 29/598 2l9/78219787 310/234 a plurality of electrode bars whose number is equal to 51lm. c1 .1 min 43/00 the umber the fingers and which have at their 581Field of Search 29/597, 598, 205 CM, gaging end a recess Of a depthwhich is 29/205 C 78 310/234 proximately equal to the diameter of thecomductor, i and while continuing to apply that pressure, supplying [56]References Chad to the electrode bars either equal valued currentssimultaneously, or successively reduced currents se- UNITED STATESPATENTS quentially for electrically connecting the fingers with3,045,103 7/1962 Warner 219/78 the conductors 3,368,054 2/1968 Brunner2,400,590 5/1946 Meyerhoefer 29/597 15 Claims, 6 Drawing Figures APPLICA 7'0? T i 1" 774150 PA I? cums/v r I S U PPL y mm METHOD FOR MAKINGARMATURE-COMMUTATOR ASSEMBLY HAVING ARMATURE WINDING OF VERY SMALLDIAMETER This application is a continuation-in-part of our copendingapplication, Ser. No. 810,238, filed Mar. 25, 1969, now abandoned. 1

BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This inventionrelates to apparatus and methods for making an armature which isintegrally connected with a commutator and has an armature winding wireof very small diameter, and more particularly to improvements in theapparatus and method ofjoining the armature winding to the commutatorfor providing electrical connection therebetween.

2. DESCRIPTION OF THE PRIOR ART Heretofore, various methods have beenproposed to provide an electrical connection between an armature windingand a commutator for making an armaturecommutator assembly. Of thesemethods, the soldering method is generally preferred since it ensures apositive electrical connection. Recently, a method of joining calledfusing has been developed which includes forming a wire-engaging fingerprojecting from a commutator, bending the finger in the form ofa hook,engaging an insulated-conductor of an armature winding with the finger,engaging an electrode bar with the finger from above to apply pressurethereto, supplying a current of suitable magnitude to the electrode barfor a suitable time under the above state thereby to thermally destroythe insulation covering existing on the conductor and to expose the coreconductor, and deforming the finger so that a sufficient electricalcontact can be maintained between the finger and the conductor. Althoughthis method of joining is defective with respect to the reliability ofthe electrical connection compared with the soldering method describedabove, it has great advantages in that a high working speed can beattained with high efficiency and the work can be automated.Therefore,'a further development in this technique is expected. As asmall-sized, light-weight and high-speed armature is increasinglydemanded, the fusing method must necessarily be employed when A l E E(American Institute of Electrical Engineers) Class H or Class Cheatresisting wires are used to form the armature winding. This isbecause the insulation covering ofthese wires can not completely bepeeled off with mere immersion in a solder bath or in a bath of aconventional covering peel-off agent, and as a result, a completeelectrical connection can not be obtained.

However, the fusing method described above has been defective in thatthe quality of produced armatures fluctuates widely due to a lack ofprecise control of the manufacturing process. Thus, various problemsincluding a lack of reliability of the electrical connection, lack ofstrength of the wire after fusing, and nonuniformity of the quality havearisen when an armature winding formed from a wire of very smalldiameter of, for example, less than 0.3 mm iselectrically connected witha commutator. In order to have a secure electrical connection, thefollowing conditions are requested:

1. The insulation covering should securely be thermally decomposed andpeeled off so that the clean copper surface of the core conductor can beexposed.

2. The covering material thus decomposed and peeled off should flow outof the interface between the copper forming the finger and the exposedcopper surface of the core conductor so that an intimate contact can beestablished therebetween.

3. No gap should exist between the copper forming the finger and thecopper surface of the core conductor so that the contact portion cansafely be protected against oxidization, sulfurization or any othercorrosion which gives rise to unstable flow of electricity as timeelapse. In order to satisfy these conditions, the magnitude of currentsupplied, duration of conducting the current and pressure applied in theconnecting operation must properly be selected.

However, according to the prior art fusing method described above,conductor wires 3a led out of an armature winding 3 are engaged withcorresponding fingers 5a provided on a commutator 4 as shown in FIG. 6and then these engaging portions are compressed by a flat electrode bar7 one after another for the connecting operation by supply of currenttherethrough. Thus, even when the individual engaging portions aresupplied with current of the same magnitude and applied with pressure ofthe same degree, the above conditions can not be utterly satisfied. As aresult of our investigation of the above problems, we found that agradual temperature rise took place in the commutator segments after thecurrent was first supplied. We concluded that the non-uniform finishresults from the fact that the resistance to plastic deformation ofcopper varies with the rise in temperature during the above period. Sucha phenomenon is not so marked when a wire having a relatively largediameter of more than 0.3 mm is employed and a fluctuation in quality isallowable. However, a serious problem arises from the above phenomenonwhen a wire having a small diameter of less than 0.3 mm is employed,such that even though both the currents and pressures applied to theelectrodes are the same, the section of the conductors might be reducedexcessively and the insulation covering the conductors might fail inthermal-decomposition due to variation of the resistivity to plasticdeformation of the conductors.

SUMMARY OF THE INVENTION It is therefore a primary object of the presentinvention to provide a method of making an armaturecommutator assemblyhaving an armature winding of very small diameter wire which assembly isformed by fitting an iron core having an armature winding of very smalldiameter wire wound therearound and a commutator on an armature shaftand then providing electrical connection between said armature windingand said commutator, said method comprising the steps of forming aplurality of wire-engaging fingers on said commutator, engaging aplurality of insulated conductors led out of said armature winding withsaid fingers, applying pressure simultaneously to all the engagingportions by a plurality of electrode bars whose number is equal to thenumber of said fingers and which have at their engaging end a recessportion of a depth which is approximately equal to the diameter of saidconductor, and supplying currents of the same value to said electrodebars simultaneously or supplying controlled currents successively forelectrically connecting said fingers with said conductors whilemaintaining said applied pressure.

Another object of the present invention is to provide a method of makingan armature-commutator assembly as above-mentioned in which theelectrode bars have a recess length which is smaller than the length ofsaid fingers.

Another object of the present invention is to provide a method of makingan armature-commutator assembly having an armature winding of very smalldiameter in which a further step of pre-forming a thin film oflowmelting metal on the surface of said wire-engaging fingers providedon said commutator is added to the first method described above so as toensure a positive electrical connection between said fingers and saidconductors.

According to the present invention, individual engaging portions can beplaced under the same joining conditions and the flow of the insulatingcovering as well as the exposure of the coreconductor can be promotedwithout reducing the strength of the conductor. As a result, anelectrical connection structure of high quality can be provided betweenthe armature winding and the commutator.

According to the present invention, further, the exposed surface of theconductor and the surface of the finger can be brought completely intointimate contact with each other at their joining portions so as toobtain an electrical connection structure of high quality which In themanufacture of the armature-commutator assembly described above, thearmature winding 3 is wound around the iron core 2 according to a knownmethod and the iron core 2 and the commutator 4 are fitted on and fixedto the armature shaft 1. Then, the conductors 3a led out of the armaturewinding 3 are engaged with the wire-engaging fingers a provided on thecommutator 4 and the fingers 5a are bent to hold therein the conductors3a. The commutator portion is then placed in ajoining device 6 as shownin FIG. 2. Although not shown in detail, the joining device 6 comprisesa plurality of electrode bars 7 whose number is is safe againstoxidization, sulfurization and other corrosion which give rise to anunstable flow of current through the connection with a lapse of time.

The above and other objects, features and advantages ofthe presentinvention will be apparent from the following description when taken inconjunction with the accompanying drawings.

BRIEF. DESCRIPTION OF THE DRAWING FIG. 1 is a front elevational view ofan armaturecommutator assembly made by the method of the presentinvention.

FIG. 2 is a side elevational view showing the joining process forproviding an electrical connection between the armature winding and thecommutator.

FIG. 3 is an enlarged sectional view showing the contour of the workingend of an electrode bar used in the joining process described above.

FIGS. 4 and 5 are enlarged schematic views showing the detail of thejoining process.

FIG. 6 is a partly sectional, front elevational view showing the joiningprocess in the prior art method.

Throughout FIGS. 1 to 6, like reference numerals are used to denote likeparts.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there isshown an armaturecommutator assembly made in accordance with the methodof the present invention. An iron core 2 having an armature winding 3 ofinsulated wire of very small diameter of less than 0.3 mm woundtherearound is mounted on an armature shaft 1 in coaxial relation with acommutator 4. Wire-engaging fingers 5a extend from commutator segments 5of the commutator 4, and conductors 3a ,led out of the armature winding3 engage the corresponding fingers 5a to establish an electricalconnection between the armature winding 3 and the commutator 4.

equal to the number of the fingers 5a, pressure applying means 10 suchas cylinders or cams for simultaneously moving the electrode bars 7toward and away from the fingers 5a, and a timed power source 12 forsupplying controlled currents to these electrode bars 7 either inparallel with the same value (amplitude) or sequentially withsuccessively less values, as later explained, to overcome the prior artnon-uniform heating problem. To prevent the applied pressure fromreducing the cross-section of the metal of conductor 3a excessively,each electrode bar 7 is provided at its working end with a recess 7a anda land 7b, and the depth H of the recess 7a as measured from the surfaceof the land 7b is approximately equal to the diameter D of the conductor3a. H= D (0.02 mm to 0.05 mm) is preferred. The length L of the recess7a is smaller than the length of the finger 5a. I

The electrode bars 7 are simultaneously urged by pressure applicator 10toward the fingers 5a. Thus, because of such simultaneous urging, eachelectrode bar 7 engages a respective finger 5a at a position as shown bythe solid lines in FIG. 4 and successively compresses that finger 5auntil the tip of the finger 5a abuts the outer peripheral surface of thecommutator 4 as shown by the broken lines. Such simultaneous pressing onthe fingers prevents any tilt of the commutator and is continued whilecurrent ofa suitable magnitude is supplied to the electrode bars 7simultaneously or sequentially as below explained and at either thesolid line or dotted line position of FIG. 4. The pressure andtemperature rise caused by the current deforms the respective finger 5ainto the form shown in FIG. 5. It will thus be appreciated that the tipof the finger 5a is deformed by the application of current and pressurecaused by the electrode moving closer to the commutator so that theengaging portions between the fingers 5a and the conductors 3a aresecurely placed under the same joining conditions. Immediately beforethe state shown in FIG. 5 is reached, the insulation covering 8 existingon the surface of the conductor 3a is completely thermally destroyed. Inorder to cause lateral flow of the destroyed insulation coveringmaterial so as to preclude the presence of the covering material in theinterface of the core conductor and the finger 5a joined together, thepressure applied to the conductor by the electrode must be large enoughto make the tip of the finger deformed, but not so large as toexcessively reduce the sectional shape of the conductor which results ina reduction in strength of the conductor at the connection. In order tosatisfy the above requirement, the electrode bar 7 is provided with therecess 7a whose depth is approximately equalto the diameter of theconductor. Thus, in the final stage of compression shown in FIG. 5, theland 7b of the electrode bar 7 is spaced a predetermined distance T(which is approximately equal to the thickness of the finger 5a) fromthe outer peripheral surface of the commutator 4, and the conductor 3ais not so flattened. In the course of crushing the conductor 3a, thethermally destroyed and peeled-off insulation covering 8 flows laterallyout of the interface between the conductor 3a and the finger 5a.Therefore, the core conductor is completely exposed and its surface isbrought into intimate contact with the surface of the finger 5a. The tipportion of the finger 5a is compressed by the land 7b of the electrodebar 7 and is joined intimately to the commutator segment 5 to enclosethe conductor 3a as seen in FIG. 5. Thus, an electrical connection ofhigh quality can be obtained and an armature-commutator assembly asshown in'FlG. 1 is completed.

For securing the fingers to the conductors in one embodiment, currentsof the same value are supplied by the timed current supply 12 to all theengaged portions in parallel, i.e., simultaneously so as to control thetemperature rise thereof substantially to the same degree.Alternatively, the controlled currents may be supplied from source 12sequentially, in which case control means therein determine the order ofcurrent supply to the electrode bars 7 and supply a smaller current tothe succeeding electrode bar 7 than the current supplied to thepreceding electrode bar 7 so that controlled currents of successivelyreduced values are supplied to the respective electrode bars 7 startingfrom the first electrode bar in the state in which all the fingers 5aare compressed by the corresponding electrode bars 7. Of course, in theabove embodiments during all the time that currents are applied to theelectrode 7, either simultaneously or sequentially, all the electrodesremain under substantially equal pressures as effected by applicator 12.[t is to be understood that if it were not for the fact that currents ofthe same value are applied simultaneously, or currents of successivelyless values are applied sequentially, the positions of the electrodeswould not all be the same with respect to their fingers 50 as shown inFIG. 5. However, this drawback of the prior art is overcome by thisinvention.

With respect to values of the applied pressure and currents, it shouldbe noted that these generally depend upon the size of the commutator,especially length and thickness of the finger, and type and thickness ofthe windings.

For example, the following values are exemplary for commutators andwindings in which the commutator is 8 mm diameter, 1 1 mm long withfingers that initially are spread to an overall diameter of 14 mm andare 1 mm thick and 5 mm long, while the winding has a copper wirediameter of 0.22 mm and two 8 micron thicknesses of insulation, theinner one being a polyester resin (polycarboxylic isocyanate) and theouter layer a polyamide resin:

a. Pressure simultaneously applied 25 kg/each electrode.

b. When the currents are simultaneously applied.

Currents: l70-l800 ampere/each electrode Timed: l 1 cycle (Power cycle60 c/s) Applied Pressure: 25 kg/electrode c. When the currents aresequentially applied Electrode Current Time Pressure No. (Aln pere)(Cycle kg/elcctrode 1 l750 1800 ll 25 2 1700 1750 ll 25 3 l650.- 1680 ll25 4 1620 1650 ll When the currents are sequentially supplied, it may bepossible to control the pressure or time sequentially in addition to, orin place of, the sequential control of the currents. However, since thenecessary heat quantity for fusing is represented by l RT, the currentcontrol is most effective for controlling the fusing. For this purpose,a plurality of transformers are prepared for the respective fusingcommutators and the current supplied to the electrode is controlled bychanging phase angle of a current supplied to the transformer connectedthereto.

In order that the electrical connection can be made more stable againstoxidization, sulfurization and other corrosion, the joining surfaces ofthe finger 5a and the conductor 3a must contact each other completely.The above purpose can not be attained by a method of supplying a largecurrent to the electrode bar 7 to expect fusing between the finger 5aand the conductor 3a due to partial fusion of the conductor 3a, sincethe conductor 3a has a very small diameter and would be completelymelted by such a large current. Therefore, other methods mustnecessarily be resorted to. According to the most preferable method, alow-melting metal such as tin, cadmium, zinc or lead or an alloy ofsome. of these metals may be employed so that the metal or alloy iseasily fused by the heat generated as a result of current supply, andwhen cooled to solidify, the metal or alloy provides a firm bond betweenthe joining surfaces of the finger 5a and the conductor 30. Such metalor alloy may preliminarily be coated in a thin layer on the surface ofthe wire-engaging finger 5a, and the first invention described above maybe performed to attain the desired purpose.

We claim:

1. A method of making an armature-commutator assembly having an armaturewinding of insulated wire of very small diameter which assembly isformed by fitting an iron core having an armature winding of said verysmall diameter wire wound therearound and a commutator on an armatureshaft and then providing electrical connection between said armaturewinding and said commutator, said method comprising the steps of forminga plurality of wire-engaging fingers on said commutator,

engaging a plurality of insulated wire conductors led out of saidarmature winding with engaging portions of said fingers,

deforming the engaged conductors by applying substantially equalpressure simultaneously to all the engaging portions by a plurality ofelectrode bars whose number is equal to the number of said fingers, andwhich have at their engaging end a recess portion of a depth which isapproximately equal to the diameter of said conductor, wherein each saidrecess portion is superposed over a respective one of said conductorsand by virtue of the recess portions controlled deformation of saidconductors occurs, and

supplying a substantially uniformly commutator heating controlledcurrent to said electrode bars for electrically connecting said fingerswith said conductors.

2. A method according to claim 1, which comprises a further step ofpre-forming a low-melting metal film on the surface of saidwire-engaging fingers provided on said commutator so as to ensure apositive electrical connection between said fingers and said conductors.

3. A method of making an armature-commutator assembly comprising thesteps of:

forming a plurality of conductor-engaging fingers on said commutator,

engaging a plurality of insulated conductors led out of an armaturewinding with engaging portions of said fingers formed by bending endportions of said fingers over the commutator,

applying pressure to said engaging portions simultaneously by electrodebars corresponding thereto, and

supplying successively decreasing controlled currents to said electrodebars sequentially, while maintaining said applied pressure.

4. A method according to claim 3, including limiting said pressure as itis effectively applied to the respective conductors engaged by saidfingers by using said electrode bars formed at their finger engaging endwith a recess superposing the conductor and having a depth approximatelyequal to the diameter of said conductor and having a length smaller thanthe length of said fingers.

5. A method according to claim 3, wherein the surfaces of said fingersare coated with a low-melting metal prior to engaging said fingers withsaid conductors.

6. A method of making an arniature-commutator assembly comprising thesteps of:

forming a plurality of conductor-engaging fingers on said commutator,

engaging a plurality of insulated conductors led out of an armaturewinding with engaging portions of said fingers formed by bending endportions of said fingers over the commutator,

applying pressure to said engaging portions simultaneously by electrodebars corresponding thereto wherein said pressure is limited as it iseffectively applied to the respective conductors engaged by saidengaging portions of said fingers by using said electrode bars formed attheir finger engaging end with a recess, each of which superposes arespective conductor and has a depth approximately equal to the diameterof said conductors and has a length smaller than the length of saidfingers whereby deformation of the conductors is controlled, and

supplying said electrode bars simultaneously with currents of the samevalue, while maintaining said applied pressure.

7. A method of making an armature-commutator assembly according to claim6, wherein the surfaces of said fingers are coated with a low-meltingmetal prior to engaging said fingers with said conductors.

8. A method of making an armature-commutator assembly having an armaturewinding of insulated wire of very small diameter, comprising the stepsof:

forming a plurality of conductor-engaging fingers on said commutator,coating the surfaces of said fingers with tin, engaging a plurality ofinsulated conductors led out of said armature winding with engagingportions of said fingers formed by bending end portions of said fingersover the commutator,

applying equal pressure simultaneously to all the engaging portions byelectrode bars respectively corresponding thereto to deform saidconductors,

limiting the applied pressure as it is effectively applied to saidconductors by using said electrode bars formed at the engaging endthereof with a recess superposing said conductor and having a depthapproximately equal to the diameter of said conductor wherebydeformation of said conductors is controlled, and

concurrently supplying equal valued currents to said electrode barssimultaneously for fusing said fingers with said conductors.

9. A method of making an armature-commutator assembly comprising thesteps of:

connecting a plurality of insulated conductors extending from anarmature winding to a respective plurality of projecting commutatorfingers having portions bent over the conductors and commutator to holdthe conductors between the respective fingers and commutator, and

fusion welding said fingers and conductors by simultaneously pressingeach of said fingers onto its insulated conductor and against saidcommutator with controlled limited conductor deformation andconcurrently passing current through each pressed finger and thecommutator, wherein said finger pressing is effected and effectivelylimited as to its effect on deformation of the conductors by respectiveelectrode bars each of which has a land contacting the end of the fingerand which has an adjacent recess having a depth approximately equal tothe diameter of the respective conductor for contacting the respectivefinger thereover and having a length which is less than the length ofsaid fingers, said pressing being continued until the electrode landsare spaced from said commutator a distance approximating the thicknessof said fingers,

characterized by the magnitude of the pressure effecting said pressingand the magnitude of said current for each pressed finger beingsufficiently large to completely thermally destroy and peel off theinsulation from the conductor under each pressed finger and to causelateral flow of the peeled off insulation so as to preclude the presenceof insulation in the interface of each joined conductor and finger,

said pressure magnitude being less at each finger than that whichreduces the sectional shape of the conductor so much as to reducesignificantly the strength of the condocutor at its connection to therespective finger, and

said current magnitude at each finger being less than that which causesthe temperature in the commutator at that finger to be significantlyhigher than at other fingers during the said fusion welding of all thefingers and conductors and less than that which causes complete meltingof the respective conductor. 10. A method of making anarmature-commutator assembly comprising the steps of:

connecting a plurality of insulated conductors extending from anarmature winding to a respective plurality of projecting commutatorfingers having portions bent over the conductors and commutator to holdthe conductors between the respective fingers and commutator, and

fusion welding said fingers and conductors by simultaneously pressingeach of said fingers onto its insulated conductor and against saidcommutator with controlled limited conductor deformation andconcurrently passing current through each pressed finger and thecommutator,

characterized by the magnitude of the pressure effecting said pressingand the magnitude of said current for each pressed finger beingsufficiently larger to completely thermally destroy and peel off theinsulation from the conductor under each pressed finger and to causelateral flow of the peeled off insulation so as to preclude the presenceof insulation in the interface of each joined conductor and finger,

said pressure magnitude being less at each finger than that whichreduces the sectional shape of the conductor so much as to reducesignificantly the strength of the conductor at its connection to therespective finger, and

said current magnitude at each finger being less than that which causesthe temperature in the commutator at that finger to significantly higherthan at other fingers during the said fusion welding of all the fingersand conductors and less than that which causes complete melting of therespective conductor, wherein the said passing of current through saidfingers is effected sequentially to the fingers and wherein at least oneof the later fingers in the sequence receives a said current of lesservalue than a finger earlier in the sequence to prevent commutatortemperature rise.

11. A method as in claim 9 wherein each said finger is coated with alow-melting metal before the respective insulated conductor is connectedthereto for providing a more firm fusion welded bond between therespective fingers and conductors so as to make the electricalconnection therebetween more stable against oxidization, sulfurizationand other corrosion.

12. A method of making an armature-commutator assembly comprising thesteps of:

forming a plurality of conductor-engaging fingers on said commutator,

engaging a plurality of insulated conductors led out of an armaturewinding with engaging portions of said fingers formed by bending endportions of said fingers over the commutator,

deforming the engaged conductors by applying substantially equalpressure to said engaged portions simultaneously by electrode barscorresponding thereto,

limiting the amount of said conductor deformation while said pressure isapplied by using electrode bars formed with recesses, each having adepth approximately equal to the diameter of the conductors and eachrecess superposing a respective conductor, and

supplying currents to said electrode bars while maintaining said appliedpressure.

13. A method of making an armature-commutator assembly comprising thesteps of:

forming a plurality of conductor-engaging fingers on said commutator,

coating the surface of said fingers with low-melting metal,

engaging a plurality of insulated conductors led out of said armaturewinding with said fingers bent over the circumferential periphery ofsaid commutator and said conductors to effect a finger end portionextending beyond each said conductor,

limitedly deforming said engaged conductors by applying pressuresimultaneously to all the fingers by electrode bars formed at theengaging end thereof with a land contacting a said finger end portionand with a recess having a depth approximately equal to the diameter ofthe respective conductor for contacting the respective finger thereover,and

supplying successively decreasing controlled currents to said electrodebars sequentially for fusing said fingers with said conductors, whilemaintaining said applied pressure, to thermally destroy and peel off theconductor insulation from under the fingers and cause lateral flowthereof and to flatten said finger end portions against said commutator.

14. A method of making an armature-commutator assembly comprising thesteps of:

forming a plurality of conductor-engaging fingers on said commutator,

coating the surface of said fingers with low-melting metal,

engaging a plurality of insulated conductors led out of said armaturewinding with said fingers bent over the circumferential periphery ofsaid commutator and said conductors to effect a finger end portionextending beyond each said conductor,

limitedly deforming the engaged conductors by applying pressuresimultaneously to all the fingers by electrode bars formed at theengaging end thereof with a land contacting a said finger end portionand with a recess having a depth approximately equal to the diameter ofthe respective conductor for contacting the respective finger thereoverwith said recess superposed over said respective conductor, and

supplying equal valued currents to said electrode bars simultaneouslyfor fusing said fingers with said conductors, while maintaining saidapplied pressure, to thermally destroy and peel off the conductorinsulation from under the fingers and cause lateral flow thereof andflatten said finger end portions against said commutator.

15. A method of making an armature-commutator assembly having anarmature winding of insulated wire of very small diameter, comprisingthe steps of:

forming a plurality of conductor-engaging fingers on said commutator,

coating the surface of said fingers with tin,

engaging a plurality of insulated conductors led out of said armaturewinding with engaging portions of said fingers,

limitedly deforming said engaged conductors by applying pressuresimultaneously to all the engaging portions by electrode barsrespectively corresponding thereto, each of said electrode bars beingformed at the engaging end thereof with a recess having a depthapproximately equal to the diameter of said conductor, and

supplying successively decreasing currents to said electrode barssequentially for fusing said fingers with said conductors, whilemaintaining said applied pressure.

1. A method of making an armature-commutator assembly having an armaturewinding of insulated wire of very small diameter which assembly isformed by fitting an iron core having an armature winding of said verysmall diameter wire wound therearound and a commutator on an armatureshaft and then providing electrical connection between said armaturewinding and said commutator, said method comprising the steps of forminga plurality of wire-engaging fingers on said commutator, engaging aplurality of insulated wire conductors led out of said armature windingwith engaging portions of said fingers, deforming the engaged conductorsby applying substantially equal pressure simultaneously to all theengaging portions by a plurality of electrode bars whose number is equalto the number of said fingers, and which have at their engaging end arecess portion of a depth which is approximately equal to the diameterof said conductor, wherein each said recess portion is superposed over arespective one of said conductors and by virtue of the recess portionscontrolled deformation of said conductors occurs, and supplying asubstantially uniformly commutator heating controlled current to saidelectrode bars for electrically connecting said fingers with saidconductors.
 2. A method according to claim 1, which comprises a furtherstep of pre-forming a low-melting metal film on the surface of saidwire-engaging fingers provided on said commutator so as to ensure apositive electrical connection between said fingers and said conductors.3. A method of making an armature-commutator assembly comprising thesteps of: forming a plurality of conductor-engaging fingers on saidcommutator, engaging a plurality of insulated conductors led out of anarmature winding with engaging portions of said fingers formed bybending end portions of said fingers over the commutator, applyingpressure to said engaging portions simultaneously by electrode barscorresponding thereto, and supplying successively decreasing controlledcurrents to said electrode bars sequentially, while maintaining saidapplied pressure.
 4. A method according to claim 3, including limitingsaid pressure as it is effectively applied to the respective conductorsengaged by said fingers by using said electrode bars formed at theirfinger engaging end with a recess superposing the conductor and having adepth approximately equal to the diameter of said conductor and having alength smaller than the length of said fingers.
 5. A method according toclaim 3, wherein the surfaces of said fingers are coated with alow-melting metal prior to engaging said fingers with said conductors.6. A method of making an armature-commutator assembly comprising thesteps of: forming a plurality of conductor-engaging fingers on saidcommutator, engaging a plurality of insulated conductors led out of anarmature winding with engaging portions of said fingers formed bybending end portions of said fingers over the commutator, applyingpressure to said engaging portions simultaneously by electrode barscorresponding thereto wherein said pressure is limited as it iseffectively applied to the respective conductors engaged by saidengaging portions of said fingers by using said electrode bars formed attheir finger engaging end with a recess, each of which superposes arespective conductor and has a depth approximately equal to the diameterof said conductors and has a length sMaller than the length of saidfingers whereby deformation of the conductors is controlled, andsupplying said electrode bars simultaneously with currents of the samevalue, while maintaining said applied pressure.
 7. A method of making anarmature-commutator assembly according to claim 6, wherein the surfacesof said fingers are coated with a low-melting metal prior to engagingsaid fingers with said conductors.
 8. A method of making anarmature-commutator assembly having an armature winding of insulatedwire of very small diameter, comprising the steps of: forming aplurality of conductor-engaging fingers on said commutator, coating thesurfaces of said fingers with tin, engaging a plurality of insulatedconductors led out of said armature winding with engaging portions ofsaid fingers formed by bending end portions of said fingers over thecommutator, applying equal pressure simultaneously to all the engagingportions by electrode bars respectively corresponding thereto to deformsaid conductors, limiting the applied pressure as it is effectivelyapplied to said conductors by using said electrode bars formed at theengaging end thereof with a recess superposing said conductor and havinga depth approximately equal to the diameter of said conductor wherebydeformation of said conductors is controlled, and concurrently supplyingequal valued currents to said electrode bars simultaneously for fusingsaid fingers with said conductors.
 9. A method of making anarmature-commutator assembly comprising the steps of: connecting aplurality of insulated conductors extending from an armature winding toa respective plurality of projecting commutator fingers having portionsbent over the conductors and commutator to hold the conductors betweenthe respective fingers and commutator, and fusion welding said fingersand conductors by simultaneously pressing each of said fingers onto itsinsulated conductor and against said commutator with controlled limitedconductor deformation and concurrently passing current through eachpressed finger and the commutator, wherein said finger pressing iseffected and effectively limited as to its effect on deformation of theconductors by respective electrode bars each of which has a landcontacting the end of the finger and which has an adjacent recess havinga depth approximately equal to the diameter of the respective conductorfor contacting the respective finger thereover and having a length whichis less than the length of said fingers, said pressing being continueduntil the electrode lands are spaced from said commutator a distanceapproximating the thickness of said fingers, characterized by themagnitude of the pressure effecting said pressing and the magnitude ofsaid current for each pressed finger being sufficiently large tocompletely thermally destroy and peel off the insulation from theconductor under each pressed finger and to cause lateral flow of thepeeled off insulation so as to preclude the presence of insulation inthe interface of each joined conductor and finger, said pressuremagnitude being less at each finger than that which reduces thesectional shape of the conductor so much as to reduce significantly thestrength of the condocutor at its connection to the respective finger,and said current magnitude at each finger being less than that whichcauses the temperature in the commutator at that finger to besignificantly higher than at other fingers during the said fusionwelding of all the fingers and conductors and less than that whichcauses complete melting of the respective conductor.
 10. A method ofmaking an armature-commutator assembly comprising the steps of:connecting a plurality of insulated conductors extending from anarmature winding to a respective plurality of projecting commutatorfingers having portions bent over the conductors and commutator to holdthe conductors between the respective fingers and commutator, and fusIonwelding said fingers and conductors by simultaneously pressing each ofsaid fingers onto its insulated conductor and against said commutatorwith controlled limited conductor deformation and concurrently passingcurrent through each pressed finger and the commutator, characterized bythe magnitude of the pressure effecting said pressing and the magnitudeof said current for each pressed finger being sufficiently larger tocompletely thermally destroy and peel off the insulation from theconductor under each pressed finger and to cause lateral flow of thepeeled off insulation so as to preclude the presence of insulation inthe interface of each joined conductor and finger, said pressuremagnitude being less at each finger than that which reduces thesectional shape of the conductor so much as to reduce significantly thestrength of the conductor at its connection to the respective finger,and said current magnitude at each finger being less than that whichcauses the temperature in the commutator at that finger to significantlyhigher than at other fingers during the said fusion welding of all thefingers and conductors and less than that which causes complete meltingof the respective conductor, wherein the said passing of current throughsaid fingers is effected sequentially to the fingers and wherein atleast one of the later fingers in the sequence receives a said currentof lesser value than a finger earlier in the sequence to preventcommutator temperature rise.
 11. A method as in claim 9 wherein eachsaid finger is coated with a low-melting metal before the respectiveinsulated conductor is connected thereto for providing a more firmfusion welded bond between the respective fingers and conductors so asto make the electrical connection therebetween more stable againstoxidization, sulfurization and other corrosion.
 12. A method of makingan armature-commutator assembly comprising the steps of: forming aplurality of conductor-engaging fingers on said commutator, engaging aplurality of insulated conductors led out of an armature winding withengaging portions of said fingers formed by bending end portions of saidfingers over the commutator, deforming the engaged conductors byapplying substantially equal pressure to said engaged portionssimultaneously by electrode bars corresponding thereto, limiting theamount of said conductor deformation while said pressure is applied byusing electrode bars formed with recesses, each having a depthapproximately equal to the diameter of the conductors and each recesssuperposing a respective conductor, and supplying currents to saidelectrode bars while maintaining said applied pressure.
 13. A method ofmaking an armature-commutator assembly comprising the steps of: forminga plurality of conductor-engaging fingers on said commutator, coatingthe surface of said fingers with low-melting metal, engaging a pluralityof insulated conductors led out of said armature winding with saidfingers bent over the circumferential periphery of said commutator andsaid conductors to effect a finger end portion extending beyond eachsaid conductor, limitedly deforming said engaged conductors by applyingpressure simultaneously to all the fingers by electrode bars formed atthe engaging end thereof with a land contacting a said finger endportion and with a recess having a depth approximately equal to thediameter of the respective conductor for contacting the respectivefinger thereover, and supplying successively decreasing controlledcurrents to said electrode bars sequentially for fusing said fingerswith said conductors, while maintaining said applied pressure, tothermally destroy and peel off the conductor insulation from under thefingers and cause lateral flow thereof and to flatten said finger endportions against said commutator.
 14. A method of making anarmature-commutator assembly comprising the steps of: forming aplurality of conductor-eNgaging fingers on said commutator, coating thesurface of said fingers with low-melting metal, engaging a plurality ofinsulated conductors led out of said armature winding with said fingersbent over the circumferential periphery of said commutator and saidconductors to effect a finger end portion extending beyond each saidconductor, limitedly deforming the engaged conductors by applyingpressure simultaneously to all the fingers by electrode bars formed atthe engaging end thereof with a land contacting a said finger endportion and with a recess having a depth approximately equal to thediameter of the respective conductor for contacting the respectivefinger thereover with said recess superposed over said respectiveconductor, and supplying equal valued currents to said electrode barssimultaneously for fusing said fingers with said conductors, whilemaintaining said applied pressure, to thermally destroy and peel off theconductor insulation from under the fingers and cause lateral flowthereof and flatten said finger end portions against said commutator.15. A method of making an armature-commutator assembly having anarmature winding of insulated wire of very small diameter, comprisingthe steps of: forming a plurality of conductor-engaging fingers on saidcommutator, coating the surface of said fingers with tin, engaging aplurality of insulated conductors led out of said armature winding withengaging portions of said fingers, limitedly deforming said engagedconductors by applying pressure simultaneously to all the engagingportions by electrode bars respectively corresponding thereto, each ofsaid electrode bars being formed at the engaging end thereof with arecess having a depth approximately equal to the diameter of saidconductor, and supplying successively decreasing currents to saidelectrode bars sequentially for fusing said fingers with saidconductors, while maintaining said applied pressure.